A 36th birthday, a year off - two months of which was spent in jail last summer on a domestic abuse conviction - would normally be the recipe for disaster for any fighter taking on a quality opponent. But Floyd Mayweather Jr, the pound-for-pound king, is not just any fighter. Instead, he looked the way he always looks: dominant.

Mayweather easily retained the world welterweight championship with a masterful one-sided beatdown of interim titlist Robert Guerrero on Saturday night before a crowd of 15,880 at the MGM Grand Garden Arena.

Guerrero had called out for Mayweather to fight him for the past couple of years, and you know what they say: Be careful what you wish for.

Mayweather appeared vulnerable in his previous fight, when he was tagged repeatedly in a unanimous decision win against Miguel Cotto last May, leading some to suggest that perhaps Mayweather's years of dominance were coming to a close. But after he took apart a man who was six years younger, physically bigger and unafraid to try to rough him up, forget about it.

It was all Mayweather. All three judges, Jerry Roth, Duane Ford and Julie Lederman, scored it 117-111 for Mayweather. ESPN.com had it 119-109 for the champion.

The fight was the first for Mayweather under a 30-month deal he signed with Showtime/CBS - after dumping longtime TV home HBO - that could see him fight up to six times and earn $200 million-plus. His next date is September 14, also at the MGM Grand, and if Mayweather continues to perform as he did against Guerrero, it could be a deal well worth the investment, because "Money" dazzled - and earned a minimum of $32 million, tying his own record for biggest purse in boxing history.

Mayweather rarely got hit cleanly, a testament to his father, Floyd Mayweather Sr, a defensive-minded trainer who returned to head his son's corner for the first time since a junior lightweight title defence in 2001. They have been estranged on and off for years while Floyd Jr's uncle Roger Mayweather served as his trainer. But with Roger increasingly feeling the effects of diabetes and Floyd Jr realising he needed to go back to his defensive basics, the match worked.

"I was really happy to be back with my father," Mayweather said. "I knew after the Cotto fight, I was getting hit too much and my dad would help me get hit less. My defence was on point, and he told me just stick to your defence - the less you get hit, the better - and to box smart."

Floyd Sr, who kept a relatively low profile during the promotion, was pleased with how his son fought. "I thought Floyd did an excellent job," he said. "I helped bring back the defence because I thought he was getting hit too much. There was nothing he couldn't do in there anyway tonight. But after the Cotto fight, he came to me and said, 'Please train me. I feel like I'm getting hit too much.' Honestly, Floyd could have danced the whole fight, but instead he used his defensc and I told him to steal him with the right hand. That was the shot [Guerrero] couldn't see."

Guerrero had modest success in the first two rounds, but by the third, Mayweather had him figured out and began to crank up his straight right hand, which he landed often before moving out of the way. On and on it went as Mayweather (44-0, 26 KOs), of Las Vegas, landed clean right hands against the southpaw Guerrero, who showed a great chin but little ability to land anything solid in return.

He tried to corner Mayweather and impose his bigger body on him, but it didn't work. The elusive Mayweather moved his head or danced away.

But for all the talk from Mayweather about defence after the fight, his offence deserved as much attention. He landed 195 of 476 punches (41 per cent), according to CompuBox statistics, while limiting Guerrero to landing 113 of 581 blows (19 per cent). Mayweather connected on an extremely high 60 per cent of his power shots (153 of 254).

He barely threw any left hands, beating Guerrero (31-2-1, 18 KOs), 30, basically with one hand, which his father noticed. "I was hoping he would throw more hooks behind the right, but he hasn't fought in a year," Floyd Sr said. "He did the majority of everything he could and he tried to do a lot of different things. He did a great job, and I am happy to be back in his corner."

Mayweather landed a steaming right hand in the fourth round to rock Guerrero, who stayed up. Guerrero had been down only once in his career, and that was a flash knockdown against Joel Casamayor in a fight Guerrero easily won.

Mayweather, making the first defence of the 147lb title he won by fourth-round knockout of Victor Ortiz in September 2011 - he fought Cotto at junior middleweight - opened a nasty cut over Guerrero's left eye in the eighth round and finished the round by rocking Guerrero with a clean right hand. Mayweather had a huge round, connecting on 23 of 33 power shots, according to CompuBox statistics.

Guerrero, who made a career-high $3 million, plus a share of the pay-per-view profits, must have known he needed something dramatic to happen in the 12th round, but he couldn't do much of anything. That was just as had been the case for virtually the entire fight. And just before the final bell, Mayweather - unsurprisingly - landed a clean right hand.

"Everybody was saying that because I'm 36 that I'm not sharp after the Cotto fight," Mayweather said. "Cotto is a [future] Hall of Famer. I've been in with the best. I keep wanting to give the fans exiting fights. I was looking for the knockout tonight, but I hurt my [right] hand midway through the fight. He was pressing the attack, but I had good work for this fight: young, strong guys pushing me for this fight."

When the fight ended, Guerrero had the audacity to raise his hands in victory, and his father and trainer, Ruben Guerrero, hilariously shouted at press row that all Mayweather did was "run like a chicken." But the fighter was classier in defeat.

"He was barely squeaking by the punches; that's why he's undefeated," Guerrero said. "I'm still a winner, no matter what. God has a plan for me, but today it wasn't to beat Floyd Mayweather. But it was to be here in front of all these people to inspire them.

"He was barely slipping by the punches. I landed some good shots but, you know, Floyd is a great fighter. He's got great defence, he's slick, he's quick. He came out and did his thing. He was a little better than I thought. I thought I was going to catch him, but he was on his game tonight. I'm going to keep fighting. Hopefully, before Floyd Mayweather retires, I'll get that shot again. I'm going to get back in the gym and re-position to fight him again before he retires."

Guerrero, who won titles at featherweight and junior lightweight, plus two interim belts at lightweight, hadn't lost since a split decision at featherweight to Gamaliel Diaz - which he avenged by knockout - in December 2005.

Mayweather hasn't lost since Serafim Todorov of Bulgaria beat him in a controversial decision in the semi-finals of the 1996 Olympic Games in Atlanta, and it doesn't look like he is going to lose again any time soon.

His opponent for September 14 is unclear, but that date falls on Mexican Independence Day weekend and the obvious opponent is Mexican star Canelo Alvarez, the unified junior middleweight champion. That's a megafight - one that fans have been asking for. But Mayweather wouldn't address Alvarez specifically.

"We don't know who we're going to fight now," he said. "Let me go home and rest now. Tonight I had a good tough battle with Robert Guerrero.

There will be plenty of time in the coming days and weeks for Mayweather, still the best in the world, to think about who he will give the opportunity to knock him off that pedestal.